Project Summary/Abstract T follicular helper cells (Tfh) are a type of immune system cell that provide critical support in the generation of antibodies during vaccination. Understanding the mechanism by which these cells support highly efficacious and durable vaccine responses could assist in the development of novel vaccines targeting diseases such as malaria. Most of our knowledge on the characteristics and function of Tfh has come from basic immunology research done in mice. To study Tfh responses in mice, the convention has been to sample specialized immune tissues such as lymph nodes and spleen. In humans, these tissues are not readily accessible for study, so human immunologists study blood Tfh responses. Unfortunately, blood Tfh are thought to travel to lymphoid tissue when their relevant antigen enters the body. Thus, study of Tfh responses in blood is unlikely to reveal the helper T cell functions during vaccination that lead to the antibodies that provide protective immunity. The proposed project aims to characterize the Tfh response in both blood and lymphoid tissue in mouse and human hosts in response to vaccination. The goal of this work will be to determine whether measuring blood Tfh can be reliably used to study lymph node Tfh responses in human studies. During this study we will develop and optimize highly innovative techniques including vaccine-specific Tfh cell tracking, combined with lymph node mapping and serial lymph node sampling. These techniques will be used to track vaccine specific Tfh responses at their primary site of action. This project will serve as the foundation for future Tfh studies of vaccines, providing key technologies for studying Tfh and knowledge about Tfh localization during a vaccine response. These tools and knowledge will then be used to study Tfh responses in malaria vaccines, which have low efficacy in field-based studies. The goal of these future studies will be to inform novel vaccine design and administration protocols in pursuit of a highly efficacious malaria vaccine.